Fuel cost = distance ÷ MPG × price per gallon. A 300-mile drive in a car that gets 28 mpg uses 10.71 gallons; at $3.50 a gallon that is $37.50 one way, or 12.5¢ per mile. Double it for a round trip and divide by the number of people sharing the ride.
For a yearly figure, the calculator uses the same 15,000-mile annual assumption that EPA uses on new-vehicle fuel economy labels. The $3.50 default is only an example; enter the price you actually pay.
How to use the fuel cost calculator (gas trip cost)
- Enter the one-way distance in miles or kilometers.
- Enter the car's fuel economy in miles per gallon. (If you know L/100 km, convert with the MPG calculator: mpg = 235.21 ÷ L/100 km.)
- Enter the price per gallon.
- Choose one way or round trip and how many people are splitting the cost.
Formula
Worked example
300 miles each way, 28 mpg, $3.50/gal, round trip, 3 people.
- 300 ÷ 28 = 10.714 gal one way; round trip 21.43 gal.
- 21.43 × $3.50 = $75.00 round trip ($37.50 one way).
- Per person: $75.00 ÷ 3 = $25.00. Per mile: $3.50 ÷ 28 = $0.125.
- A year of driving at 15,000 mi: 535.7 gal × $3.50 = $1,875.
How MPG changes the cost
| MPG | Gallons per 300 mi | Cost at $3.50 | Per year (15,000 mi) |
|---|---|---|---|
| 20 | 15.0 | $52.50 | $2,625 |
| 25 | 12.0 | $42.00 | $2,100 |
| 30 | 10.0 | $35.00 | $1,750 |
| 40 | 7.5 | $26.25 | $1,313 |
| 50 | 6.0 | $21.00 | $1,050 |
EPA's combined MPG weights city driving 55% and highway 45%, so a mostly-highway trip may use less fuel than the combined figure suggests, and city or heavily loaded driving more. To measure your real MPG from a fill-up, use the mpg calculator (gas mileage). Fuel is only part of the cost of driving; financing is covered in the auto loan calculator.
Using metric units
If your car's consumption is in liters per 100 km and fuel is priced per liter, the formula is cost = distance (km) × L/100 km ÷ 100 × price per liter. Example: 500 km at 7 L/100 km uses 35 L; at €1.80/L that is €63. To use this calculator with metric figures, convert L/100 km to mpg (mpg = 235.21 ÷ L/100 km) and the price per liter to per gallon (× 3.785), or enter the distance in km and use the mpg calculator (gas mileage) conversions.
Planning a road trip budget
- Map the route and note the total miles, including side trips. Add 5–10% as a personal buffer for detours if you like.
- Use a realistic MPG: your measured figure, or the combined rating if you drive a similar mix of city and highway.
- Check fuel prices along the route; they can differ a lot between areas.
- Run the numbers for one way and round trip, then split the cost with passengers if you share.
Fuel cost per mile is also a quick way to compare driving with other options: at 12.5¢ a mile, a 600-mile round trip costs $75 in fuel, before tolls and parking.
Caveats and assumptions
- Fuel only — not tolls, parking, wear or depreciation.
- Real-world MPG varies with speed, load, weather and terrain.
- The default gas price is an example, not a current average.
Frequently asked questions
How do I calculate gas cost for a trip?
Divide the miles by your car's MPG to get gallons, then multiply by the price per gallon. 300 mi ÷ 28 mpg × $3.50 = $37.50.
How much gas does a 100-mile trip use?
100 ÷ MPG. At 25 mpg that is 4 gallons; at 40 mpg, 2.5 gallons.
What is my fuel cost per mile?
Price per gallon ÷ MPG. At $3.50 and 28 mpg, 12.5 cents per mile.
How many miles a year does EPA assume?
EPA's fuel economy labels assume 15,000 miles a year for the annual fuel cost estimate.
How do I split gas money?
Calculate the total fuel cost (round trip if everyone returns together) and divide by the number of people sharing.
How do I calculate fuel cost in liters and kilometers?
Kilometers × L/100 km ÷ 100 gives liters; multiply by the price per liter.
Sources
- FuelEconomy.gov — Learn More About the Fuel Economy Label for Gasoline Vehicles — 15,000 miles per year; combined MPG weights city 55% / highway 45%
This calculator gives estimates for planning and education. Check measurements, local codes, supplier specs and your school's official policy before relying on a result. See our disclaimer and how we build and check calculators.